By contrast, 30 percent of U.S. adults are obese, according to the U.S. Centers for Disease Control and Prevention (photo gallery: "Heavy Cost of Fat").

Experts say the obesity epidemic is spreading to children, albeit more slowly than in adults. The trend, they say, will have a huge impact on the health of China's citizens and economy.

"We're seeing a very large proportion of children and adolescents who are quite heavy and aren't moving much," said Barry Popkin, a nutrition professor at the School of Public Health at the University of North Carolina in Chapel Hill.

Popkin collaborates on an ongoing health-and-nutrition survey of 16,000 households in China. He says more kids today are overeating and putting on weight "quite quickly."

In just ten years China's childhood obesity rate has doubled, with the greatest gains coming in urban areas.

Official figures suggest that, on average, 8.1 percent of kids in urban areas are obese, compared to 3.1 percent in rural areas.